Industrial monitoring systems often employ thermal, or infrared (IR), imaging devices, which are preferably mounted in a fixed location to capture IR images of a target, which may be a particular portion of a piece of manufacturing equipment and/or a product in the midst of a manufacturing process. These devices are typically adapted to communicate with a remote monitoring station and, in some instances, are integrated with a process control package.
In harsh industrial environments it is often necessary to contain these imaging devices within a protective enclosure that keeps the imaging device cool and free of contaminations such as dust particles. The enclosure necessarily includes a window through which the thermal imaging device can view the target in the environment over a period of time.
In an explosion-proof housing, a protection grid must be used to protect the window from the external environment. The protective grid is typically constructed of steel bars which partially block the thermal imager's field of view (FOV). The shape and spacing of the bars is typically chosen with no consideration of the device located within the protective housing. As a result, the protective grid causes a strong, non-uniform attenuation pattern in the FOV thereby making the thermal measurements of the thermal imager non-radiometric.
It is desirable to design a protective grid that would produce an attenuation pattern of predictably low variation, uniformly distributed across the FOV which can be compensated for with a single transmissivity factor to keep the measurements radiometric.